Changes in soft tissue elasticity are usually related to pathological processes. Because of this, palpation is still widely used for diagnosis. Efficacy, however, is limited to abnormalities located relatively close to the skin surface. The fundamental goal of elasticity imaging is to develop surrogate, remote palpation. Using sensitive ultrasound speckle tracking procedures, controlled surface deformations, and quantitative reconstruction algorithms developed over the first funding period, elasticity imaging has emerged as a potentially new diagnostic modality providing information about the mechanical properties of internal organs. In particular, results of studies during the first funding period support the hypothesis that changes in kidney elasticity due to renal damage and concomitant scarring can be detected with elasticity imaging before problems are identified by traditional diagnostic techniques such as laboratory measurements of renal function. Based on these results, a research plan has been developed to address the important clinical problem of noninvasively detecting kidney transplant rejection. The proposed program includes fundamental studies of both optimal elasticity imaging methods and kidney elasticity. In addition, an elasticity imaging system appropriate for clinical studies will be designed and built to monitor the internal elastic properties of the transplanted kidney. This system will be tested on a group of human subjects with normally functioning renal allografts. Results from this group will be compared to elasticity images from a different group with abnormally functioning allografts. The overall program is designed to critically test the hypothesis that elasticity imaging can noninvasively detect fibrosis in a renal allograft well before functional measurements sense abnormalities.